This present application relates to startup control of gas turbine engines. More specifically, but not by way of limitation, the present application relates to methods and systems for modulating turbine rotor acceleration/velocity in the startup of a gas turbine based on a subsequently made calculation of the remaining time until the startup sequence is completed.
Generally, combustion or gas turbine engines (hereinafter “gas turbines”) include compressor and turbine sections in which rows of blades are axially stacked in stages. Each stage typically includes a row of circumferentially-spaced stator blades, which are fixed, and a row of rotor blades, which rotate about a central turbine axis or shaft. In operation, generally, the compressor rotor blades are rotated about the shaft, and, acting in concert with the stator blades, compress a flow of air. This supply of compressed air then is used within a combustor to combust a supply of fuel. The resulting flow of hot expanding combustion gases, which is often referred to as working fluid, is then expanded through the turbine section of the gas turbine. Within the turbine, the working fluid is redirected by the stator blades onto the rotor blades so to power rotation. The rotor blades are connected to a central shaft such that the rotation of the rotor blades rotates the shaft. In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which, for example, may be used to rotate the rotor blades of the compressor, so to produce the supply of compressed air needed for combustion, as well as, rotate the coils of a generator so to generate electrical power.
Many industrial applications, such as those involving power generation and aviation, still rely heavily on gas turbines, and, because of this, the engineering of more efficient engines remains an ongoing and important objective. As will be appreciated, even incremental advances in machine performance, efficiency, or cost-effectiveness are meaningful in the highly competitive marketplace that has evolved around this technology.
Related to startup operation for gas turbines and the control thereof, conventional systems and methods generally are based on defined schedules that depend upon various engine startup parameters, such as, for example, minimum/maximum fuel flow, rotor acceleration and velocity, and/or applied torque. These predefined schedules, thus, define startup characteristics for gas turbines, with certain of these startup parameters being controlled to follow paths that are predefined or fixed as part of schedules. An example of one of these predefined schedules, as discussed in more detail below, is one that defines rotor acceleration per rotor velocity. In practice, however, the startup of gas turbines regularly deviates from these nominal schedules. This, for example, may be due to variations in ambient conditions, fuel, poor closed-loop control tracking of the schedules, and/or varying performance from components or subsystems of the engine.
More specifically, gas turbine startup operation is significantly influenced by the manner in which rotor acceleration is controlled relative to rotor velocity. As will be appreciated, closed-looped control systems typically control rotor acceleration during startup operation in accordance with a schedule where rotor acceleration is a function of rotor velocity. Unfortunately, conventional startup methods and systems lack the functionality to accommodate unforeseen deviations or delays that regularly occur during the startup sequence, and these cause the duration of the process to deviate from what was originally expected or scheduled at initiation. Consequently, once deviations from the schedule occur, there is no efficient manner by which to correct or account for them. Specifically, for example, if a deviation results in the startup operation falling behind schedule, conventional methods and systems lack an efficient way by which such lost time may be “made up”, and, as would be expected, this often results startup durations that significantly vary from one occasion to the next.
These variations in startup duration negatively impact aspects of gas turbine operation and performance, as well as cost-effectiveness. For example, among other potential issues, such variations decrease component life and/or affect blade tip clearances. Further, guaranteeing startup duration for gas turbines is becoming a common contractual requirement in today's commercial environment, making such durational uncertainty highly undesirable. One approach that is commonly used to address such variation is to just include wide margins in the time allotted for engine startup. Such an approach, however, is generally undesirable due to the inefficiencies and unnecessary delays that often result. Thus, improved gas turbine startup control systems and/or methods, which provide for guaranteed startup durations with reduced margins and/or overcome any of the other above-mentioned disadvantages, would have commercial value.